Radiofrequency welding and composition of matter for impeders

ABSTRACT

An impeder device for improving the efficiency of radiofrequency welding of continuous strip metal is disclosed. The impeder device includes a housing and a layer of high permeability magnetic material mounted within a recess in the horn about which the strip material is brought into edge-to-edge engagement for the welding together of the edges thereof. A magnetic field terminator block and heat sink is provided at the upstream end of the layer of magnetic material and the housing includes fluid passages for the conduction of cooling fluid into cooling relation with the layer of magnetic material. Sintered ferrites and particulated ferromagnetic material in a resinous base are suitable for the formation of the layer of magnetic material which is constructed to provide a surface conforming to the interior surface of the strip edge portions to be joined. The composition used in the case of ferromagnetic material consists of a uniform mixture of a particulated ferromagnetic material and a resinous binder in the weight ratio range of from 5:1 to 20:1, respectively. The resinous binder is a cross-linked polyester backbone polymer.

United States Patent [72] lnventors Howard S. Cannon Evergreen Park:Phillip 1-. Catalano, Chicago; John D. Glombe, South Holland; Roger M.O'Neill, Oaklawn, all of,l1l. [21] Appl. No. 878,388 [22] Filed Nov. 20,1969 [23] Division of Ser. No. 429,726, Feb. 2, 1965,

Patent No. 3,511,957 [45] Patented June 8,1971 [73] Assignee ContinentalCan Company, Inc.

New York, N.Y.

[54] RADIOFREQUENCY WELDING AND COMPOSITION OF MATTER FOR IMPEDERS 7Claims, 9 Drawing Figs.

[52] U.S. Cl 219/85, 252/6254 [51] Int. Cl 1105b 5/10, C04b 35/04 [50]Field of Search 219/8.5, 10.43,59,102;252/62.54

[56] References Cited UNITED STATES PATENTS 2,744,040 1/1956 Altmann252/6254 X 2,933,582 4/1960 Tower 219/59 3,031,554 4/1962 Jackson.219/85 3,117,092 1/1964 Parker 252/6254 X Primary Examiner-J. V. TruheAssistant Examiner-Hugh D. Jaeger Attorney- Diller. Brown. Ramik andHolt ABSTRACT: An impeder device for improving the efficiency ofradiofrequency welding of continuous strip metal is disclosed. Theimpeder device includes a housing and a layer of highpermeabilitymagnetic material mounted within a recess in the horn about which thestrip material is brought into edgeto-edge engagement for the weldingtogether of the edges thereof. A magnetic field terminator block andheat sink is provided at the upstream end of the layer of magneticmaterial and the housing includes fluid passages for the conduction ofcooling fluid into cooling relation with the layer of magnetic material.Sintered ferrites and particulated ferromagnetic material in a resinousbase are suitable for the formation of the layer of magnetic materialwhich is constructed'to provide a surface conforming to the interiorsurface of the strip edge portions to be joined. The composition used inthe case of ferromagnetic material consists of a uniform mixture of aparticulated ferromagnetic material and a resinous binder in the weightratio range of from 5:1 to 20:1, respectively. The resinous binder is across-linked polyester backbone polymer.

PATENTEI] JUN 8 m1 sum a nr 2 FIG. 8

INVENTORS HOLDQRD S CANNON PHIUP FKCATALAN JOHN OGLQMB an ROGER MO'NEILL ATTORNIz'YS RADIOFREQUENCY WELDING AND COMPOSITION OF MATTER FORIMPEDERS This application is a division of application SER. No. 429,726,filed Feb. 2, 1965, now US. Pat. No. 3,5l|,957.

This invention relates to a composition of matter and an impeder devicehaving a high magnetic permeability for improving the efficiency ofradiofrequency welding of continuous strip metal. More specifically, theinvention relates to an impeder which is designed to be placed in thetop portion of a horn about which a tubular shape is formed in acontinuous welding line in order to provide a low reluctance path forthe magnetic flux generated by the radiofrequency induction coilsurrounding the horn and the tubular formed metal.

The impeder concentrates the magnetic flux field set up by the RFinduction coil and thereby impedes the induced current flow in sectionsof the tubular strip in which heating is not desired. By increasing theimpedance of such extraneous paths, the impeder causes the concentrationof induced current in those portions of the moving tubular metal whereheating is desired for attaining welding temperatures.

Metals, particularly aluminum, in both light-gauge (0.0066- inchthickness) and heavier gauge may be welded by lap or blap welds withincreased speeds and decreased power requirements utilizing the impederdevice of the present invention.

Some of the impeder suggested for use in continuous welding lines havebeen constructed of a solid core of ferromagnetic material, e.g., ironcores. A cylindrical-shaped impeder member contained within a portion ofthe horn about which the metal strip is formed has been used togetherwith a cooling fluid. Difficulty is encountered in such constructionswith maintaining the temperature of the impeder members below the Curietemperature, notwithstanding the presence of a coolant. Above the Curietemperature the phenomena of ferromagnetism disappears and the substancebecomes merely paramagnetic.

Another statement with respect to the employment of impeder members incontinuous welding lines is that such are unnecessary if the ratio ofthe thickness of the metal being welded to the reference depth of thecurrent or the current penetration depth inthe metal is less than 3.When the conditions are considered correct for the presence of animpeder element, a solid core of ferrimagnetic material has beenproposed. Such materials possess a permeability greater than unity atroom temperature and contain ferrous iron. An example of such materialis magnetite (Fe O which exhibits antiparallel alignment in a magneticfield. A frequently used class of ferrimagnetic materials consists ofceramic ferrites, which are made by mixing magnetite or ferrous ferritewith other metal oxides, often of the transition metal group, andsintering the resulting mixture at high temperature and pressure. Asthese materials are extremely hard and brittle ceramics, they aredifficult to machine or to form into particular shapes.

Another form of such impeder elements has been a ringshaped core offerrimagnetic material which may have fluid cooling conduits arrangedtherein. This ring-shaped core is positioned coaxially with theindirction coil which provides the heating of the continuous metaltubing being welded and hence tends to form a coupling core the thesurrounding induction coil and usually extends for only a very shortdistance along the interior of the metal tubing being formed prior towelding. A manifest impediment with such ring-shaped impeder cores isthe difficulty in cooling them. The provision of internal coolantpassages within the material is made difficult due to the fact that theymust be sintered from their component metallic oxides and are notreadily joined together for the formation of internal passages. They areextremely difficult to machine and hence passages cannot be latermachined within the material. lf such ferrimagnetic materials are to beemployed on a commercial basis they must be employed in the form ofsimple shapes which are easily manufactured during the sinteringoperation.

In addition to being constructed from materials lacking the abovedesirable properties, impeder structures used in continuous weldinglines have not been geometrically arranged to concentrate the currentinduced in those portions of the positioned material which must beheated to welding temperatures. The mere placement of impeder materialwithin and about the welding horn is insufficient answer to the problemswhich have prevented the RF line welding of thin metal stock. Specificgeometric shape and positioning, requiring machinability, are necessary.

Various cooling means have been arranged with respect to impeder membersand various support structures have been suggested by the prior art.Most supporting structures have been designed only to specificallysituate the impeder members within the forming horn. Littleconsideration has been given to the requirement of controlling theconcentration of the magnetic field intensity created by theradiofrequency induction coilor other heating device, such as electrodeshoes. The back-magnetic flux field induced within the impeder memberitself must be reduced and the flow of heat between the impeder memberand the surrounding horn metal must be eliminated. Supporting memberswhich merely connect the impeder member to the forming horn do notprovide for either of these two requirements. While the efficiency ofcontinuous tube welding in heavy gauge metals is somewhat increased bythe impeders set out in the prior art, the various factors set out abovehave not been taken into consideration in order to provide acommercially feasible welding line for thin gauge strip material.

For impeder structures, low electrical conductivity is desirable inorder to prevent eddy current flow and thus power loss. High saturationflux density, magnetic permeability, Curie temperature, thermalconductivity and good ductility and machinability are other propertieswhich, when present as a group, identify an ideal impeder substance.Presently employed impeder materials do no have all of the desirableproperties represented by adequate values to enable their use in specialemployments.

The common ferromagnetic materials, while having high magneticpermeability, also have high electrical conductivity which allows eddycurrent flow, and hence, power loss, as well as excess heating.

The sintered ferrite materials provide high permeability and relativelylow electrical conductivity; however, there is sufficient eddy currentflow in such impeder materials to present heating problems which thennecessitate special cooling techniques. The relatively low Curietemperature of such ceramic ferrite materials makes the requirement ofremoving the heat generated imperative so that the high permeabilitywill remain. These ceramic ferrites are also characterized by lowthermal conductivity which then necessitates the efficient removal ofthe heat generated by the eddy currents. ln order to remove thegenerated heat, thin cross sections of the materials are necessitated.Also, because of the relatively low saturation flux density of theceramic ferrites, a sufficient thickness of the material must beprovided to prevent saturation at high magnetic flux intensity.

The above problems with respect to the magnetic materials available havebeen overcome by providing an impeder material consisting of a mixtureof particulate ferromagnetic material with a resinous binder. Thespecific particulate materials are water-atomized iron powder andcarbonyl processed iron powders of small particle size. The impedermaterial may be cast or die pressed into particular geometric shapeswhich, when used in association with an RF welding line, permit greaterwelding speeds and efficiency. This ferromagnetic impeder material has arelatively high thermal conductivity so that it may be cooled bycontacting one surface of an impeder shape by a water cooled metallicsupport member. The material also has good machinability by whichspecific intricate shapes may be manufactured therefrom after casting ordie pressing so that particular geometric arrangement of the impeder maybe formed with respect to the associated horn.

The impeder device of the present invention consists of a magneticmaterial layer which is arranged in a surface conforming to the curvedsurface formed by the strip material when positioned for welding, asupport means for the layer and a cooling means for removing the heatgenerated within the layer by the radiofrequency alternating magneticfield. The cooling means may consist of fluid coolant channels withinthe support means or may consist of fluid coolant channels arrangedwithin a nonmagnetic housing which encloses both the magnetic materiallayer and the support means for the layer. In the description and claimsthe term magnetic material is intended to refer to those materials whichexhibit gross magnetism in a magnetic field. That is, those materialswhich are classed as ferromagnetic or ferrimagnetic. When the lattertype of magnetic material is employed the enclosed housing form of theimpeder is employed in order to give sufficient' cooling to theferrimagnetic material which has a low thermal conductivity.

It is, therefore, an object of the present invention to provide acomposition of matter suitable for use in an impeder and an impeder.

It is' a further object to provide an improvement in a radiofrequencywelding apparatus of the type which has a heat generating means and ahorn over which opposite edges and edge portions of continuous stripmaterial are positioned for welding one to another which consists of animpeder device having a magnetic material layer arranged in a surfaceconforming to the curved surface formed by the strip material whenpositioned for welding, and a support means for said layer and a coolingmeans for removing the heat generated within said layer. The impederdevice is at least partially housed in a recess formed in the horn ofthe welding apparatus and is positioned within the horn so that themagnetic material layer lies immediately under the convergingV-configuration of the strip material positioned for welding.

The magnetic material layer may be formed from either a mixture ofparticulated ferromagnetic material and a resinous hinder or aferrimagnetic material formed by sintering ferrous ferrite andtransition metal oxides into a ceramic solid.

7 The impeder device may have a magnetic field intensity terminator andheat sink block affixed to the upstream en thereof to provide formagnetic shielding and to remove heat generated therewithin.

The cooling means may be formed by an exterior nonmagnetic housingsurrounding the magnetic material layer and its support means in orderto form fluid flow channels both above and below the layer and itsassociated support or may consist of fluid flow channels connected torespective fluid ports in the support means. The former cooling means ispreferred when using the ferrimagnetic materials mentioned above.

The impeder device may be removably housed in a recess in the horn. Thedevice has a magnetic material layer arranged in a surface conforming tothe curved surface formed by the strip material when positioned forwelding and has a support means for said layer, both of which arepositioned within a nonmagnetic fluidtight housing in such a fashionthat upper and lower channels are created between the housing and thelayer and its associated support means. A coolant fluid is circulatedboth above and below the two elements encased in the nonmagnetic housingfor removing the heat generated therewithin. The impeder device isarranged within the recess in the horn so that it is immediately underthe converging V-configuration formed by the positioned strip material.The upstream end of the impeder device may consist of a magnetic fieldintensity terminator and heat sink block which is in fluidtightengagement with said housing and has first and second fluid portstherein for the circulation of the coolant fluid. The upper surface ofthe nonmagnetic housing, the magnetic material layer, and its associatedsupport are all positioned in a surface conforming to the curved surfaceformed by the strip material when positioned for welding to attain theparticular ad vantages of the present invention.

The improved radiofrequency welding apparatus, having the magneticmaterial layer, may be supported, by a support means which has fluidcoolant channels therewithin connected to first and second fluid portsfor the circulation of a coolant fluid for the extraction of generatedheat from at least one side of the magnetic material layer. The supportmeans may have a magnetic field intensity terminator and heat sink blockattached to the upstream end thereof for the purposes hereinafter setout. I

The improved impeder member for use with a radiofrequency weldingapparatus is positioned within the magnetic field generated by theheating means which is constructed of a low electrical conductivitymaterial and a high magnetic permeability material. A suitable materialhas been found to be powdered alpha-iron produced by either' thewater-atomized process or the carbonyl process, mixed in a proportion inthe range of 5:1 to 20:1 with a polyester resin.

The magnetic field intensity terminating and heat sink block may beadvantageously constructed of a high copper alloy or other goodelectrical and thermal conductivity material which can be used to form afluidtight seal with the other impeder elements.

The radiofrequency current heating means may be either an induction coilwound about said horn and spaced therefrom or electrode welding shoescontacting the edge portions of the strip material as it passes towardthe forging rolls, both connected to a source of radiofrequency current.

The radiofrequency welding apparatus may include means to continuouslyfeed strip material for welding and a horn about which the stripmaterial may be positioned for welding and includes forging rolls forforming a line of weld between the edge portions of the metal strip,with the improved structure of a radiofrequency induction coil woundabout said horn spaced therefrom, a magnetic material layer positionedwithin the cross section of said forming horn and underlying theconverging V-configuration of the strip material to concentrate themagnetic field intensity generated by said induction coil. The magneticlayer is positioned from a plane immediately upstream from the forgingrolls to a plane upstream past the opposite end of the induction coil.The magnetic material layer is formed of a ferromagnetic orferrimagnetic material arranged in a curved surface conforming to thecurved surface formed by the strip material when positioned for welding.A magnetic field intensity terminator and heat sink block may be affixedto the end of the layer to terminate the magnetic flux and to act as aheat sink. A nonmagnetic housing may cooperate with the magnetic fieldintensity terminator and heat sink block to form a fluidtight enclosurewithin which a coolant material may be circulated to cool said magneticmaterial layer.

The nonmagnetic housing and the magnetic field intensity terminator andheat sink material of the above object preferably cooperate to form aunit shaped on the bottom to fit the contour of the recess of the hornand curved on the topside thereof to complete the circular cross sectionof the horn.

The impeder and magnetic field intensity terminator block apparatus ofthe instant invention will be described in greater detail and will bemore readily understood by reference to the following description andclaims taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of the welding apparatus with parts thereofshown in sectional view;

FIG. 2 is a cross-sectional view of the apparatus of FIG. 1 taken on theline 2-2;

FIG. 3 is a perspective view taken from the underside of the impederdevice of the present invention;

FIG. 4 is a cross-sectional view of the impeder device of FIG. 3 takenon the line 4-4;

FIG. 5 is a cross-sectional view of the magnetic field intensityterminator and heat sink block of the impeder device of FIG. 4 taken online 5-5;

FIG. 6 is a perspective view of a modification of the impeder deviceshown in FIG. 3;

FIG. 7 is a cross-sectional view of the impeder device of FIG. 6 takenon the line 7-7;

device shown in Figure 6 taken on line 8-8 of FIG. 7; and

FIG. 9 is an exploded perspective view of the impeder device shown inFIG. 6. 1

Referring now to HO. 1, a portion of a forming horn is shown togetherwith forging rolls 22 and 24 which are positioned at the apex of theV-configuration formed by the converging edge portions 26 and 28 of thesheet material 30. In addition to bottom'forging roll 22 and top forgingroll 24, forming horn 20 includes a conventional fluid entry and/or exitconduit assembly 32 for supplying lubricant and coolant liquids to thebearings in various rolls such as bottom forging roll 22 as well assupplying material for an inside lacquer strip to cover the inside weldseam.

Forming horn 20, in accordance with the instant invention, includes apair of fluid lines 34 in the upper portion. A top support roll 36 isshown enclosed within a portion of forming horn 20 and a cooperatinglower support roll 38 is shown connected to a supporting means 40.

Supporting rolls 36 and 38 are part of the means for advancing thetubular formed sheet material over the forming horn 20 and maintainingthe tubular form.

A parting or spacing roll 42 is shown located in the uppermost portionof forming horn 20 and positioned to a spacer member for strip edgeportions 26 and 28. The strip material 30 advances over forming born 20and in a downstream direction toward forging rolls 22 and 24. The metaledge portions 26 and 28 are heated by the radiofrequency induction coil44 wound about forming born 20 and spaced therefrom a sufficientdistance to accommodate the passage of tubular formed strip material 30.Induction coil 44 is connected to a source of radiofrequency current(not shown). The apex of the V-configuration formed by the edges or edgeportions 26 and 28 is located immediately between forging rolls 22 and24. The heated edge portions are brought together between forging rolls22 and 24 and a line or weld 46 is formed. The resulting product is acontinuously formed tubular structure having a single weld seam therein.By proper te'nsioning ofthe tubular formed material 30 and bypositioning the edge portions 26 and 28 with respect to one another,either a lap or a blap weld seam may be formed. in both types of weldseam it is necessary that the forging rolls immediately contact thejoined edge portions at or in close proximity, downstream, of the apexof the V-configuration.

Forming horn 20 is constructed with a recess 48 in the upper portionthereof immediately underlying the helical induction coil 44. An impederdevice 50 rests in recess 48 and extends within said recess to the closeproximity of forging rolls 22 and 24. The impeder device 50 extendscompletely through the length of induction coil 44 and immediatelyunderlies the edge portions 26 and 28 and extends from a point close tospacing roll 42 to within a short distance from forging rolls 22 and 24,and therewith extends under the converging V-conflguration up to theclose proximity of the apex.

impeder device 50 has a nonmagnetic housing 52 and a magnetic fieldintensity terminator and heat sink end block 54 affixed to housing 52 atthe upstream end thereof. The connection between housing 52 and block 54is watertight to provide for circulation of a coolant fluid through thehousing. A first fluid port 56 extends through block 54 and intocommunication with the interior of the housing 52 while a second fluidport 58 extends through block 54 to provide an exit for the coolantfluid within housing 52. The flow of the coolant fluid may be reversedso that port 58 becomes the entry port and port 56 becomes the exitport.

impeder device 50 is more clearly shown by the enlarged cross-sectionalview of FIG. 2 in which the forming horn 20 is positioned withininduction coil 44. Recess 48 in forming horn 20 provides support forimpeder device 50. Strip material or the tubular formed sheet material30 is shown positioned around the horn and out of contact with horn 20and the associated impeder device 50. Edges or edge portions 26 and 28are seen converging to the apex 60 which is immediately under forgingroll 24.

Nonmagnetic housing 52 has a bottom panel or portion 62 connected to asemicylindrical covering or top portion'64 through horizontal sideskirts 66 and 68. The channel shaped recess 48 provides a stable supportfor impeder device 50 due to the configuration of the bottom panel 62and horizontal side skirts 66 and 68. Within housing 52 a magneticmaterial layer 70 is supported by a semicylindrical support member 72.The magnetic material layer 70 is composed of individual magneticmaterial elements 74, but may be a continuous unitary element, ifdesired. The employment of individual thin rectangular elements for themagnetic material is facilitated by the availability of sintered ceramicferrite strips in the present market.

impeder device 50 has a downstream end 76 composed of a similarnonmagnetic material to that from which bottom panel 62, top portion 64and horizontal side skirts 66 and 68 are constructed. Fluid flowchannels 78 are shown cut into the material of end panel or wall 76 andmay be molded and placed simultaneously with the construction of endpanel or wall 76.

FIG. 3 shows end panel 76 in fluid tight engagement with the nonmagnetichousing 52, which is in turn in fluidtight engagement with the upstreamend block 54. Fluid flow channels 78 may be seen on the interior wall ofend panel 76. Bottom panel 62 has a tapered downstream end 80 whichdecreases in width from angular connection 82 to the connection ofhousing 52 to end panel 76. Of course, the bottom panel 62, side skirts66 and 68 and top panel 64 may be integrally molded as a unitary pieceor separately manufactured and assembled.

Side skirts 66 and 68 slope upwardly from angular connection 82 intoengagement with the horizontally extending side portions 84 and 86 ofend panel 76. The overall configuration of the undersurface of impederdevice 50 is such that it may be secured in position within recess 48which provides a stable support therefor. That is, recess 48 isconfigured in a manner so that the reduced tapered portion 80 of bottompanel 62 and the elevated side skirts 66 and 68 engage the recess tolock the impeder device 50in place in horn 20.

By FIG. 4 the flow of coolant fluid through impeder device 50 may beunderstood. Fluid coolant is forced into port 56 which extends throughend block 54 and into communication with the interior of non magnetichousing 52. semicylindrical support member 72 and bottom panel 52 form afluid flow channel for the passage of the fluid coolant toward thedownstream end panel 76. The fluid coolant then passes through fluidchannels 78 and onto the upper surface of magnetic material layer 70 andflows therealong to the upstream end of the magnetic material layer 70and then into a semicylindrical receiving port 88. This port is thenconnected to internal channel which is provided with a connection to thesecond fluid port 58, of FIG. 1. The raised side skirt 66 of the impederdevice is shown extending from angular connection 82 upwardly to endpanel 76. Top panel 64 is shown in a stepped engagement to magneticfield intensity terminating and heat sink block 54 and in a overlyingrelationship to downstream end panel 76. The bottom panel 62 is securedto block 54 by a threaded securing means 92. All connections of thevarious parts of impeder device 50 are of a fluidtight type in order toretain coolant fluid.

Magnetic material layer 70 may be affixed to support member 72 by achemical securing means such as glue or maybe unsecured as thecooperative spacing of support member 72 and top panel 64 preventrelative movement of the magnetic material layer 70 with respect to theother fixed parts of the impeder device.

FIG. 5 shows the flow path of the fluid coolant from semicylindricalport 88 into internal channel 90 which has a reduced upper portion 94.The fluid is then caused to flow into exit channel 96 and then intofluid port 58 which extends through the block 54 to connect with exitchannel 96. The magnetic material layer 70 is shown consisting ofindividual elements 74, as in FIG. 2. Threaded securing means 92-forsecuring block 54 with the bottom panel 62 of FIGS. 2-4 are shown bydotted lines under the magnetic material layer 70.

The material from which the magnetic layer 70 is constructed may beeither a ferromagnetic material of a ferrimagnetic material, that is, amaterial which exhibits gross magnetism when placed in a magnetic fieldof sufficient intensity. Many of the numerous ferromagnetic materialsare undesirable when used for this magnetic layer associated with theradiofrequency induction coil 44. Common transformer core iron has ahigh electrical conductivity and, hence, when used for the magneticlayer 70, does not have a high volume resistivity by which eddy currentsare prevented from flowing in the iron. Therewith, the iron attains avery high temperature which is difficult to control even with thecooling fluid passing under and over the thin section. Associated withthis heat buildup, there is a concomitant power loss from the inductioncoil 44.

A ferromagnetic material which presents a unique solution to the aboveeddy current losses encapsulates small iron particles in a resinousbinder matrix so that they are isolated one from another and do not havea current flow therebetween. The iron particles may be made by any ofthe many wellknown processes for iron powder production. Carbonylprocessed iron and water-atomized iron powders have been used with goodresults. Several grades of carbonyl processed iron have been used inmagnetic layer 70: (l the 0.18 percent carbon grade-a particle size of8-microns average; (2) the 0.05 percent maximum carbon content grade--anaverage particle size of microns; and (3) a second type havingapproximately 0.05 percent carbon content and having a 0.8- micronaverage diameter. Generally the second grade of this carbonyl powder ispreferred.

' The resinous material which may be used as a binding matrix may beeither a thermoplastic or a thermosetting material. Therewith, poly(methylmethacrylate) may be used under carefully controlled mixingconditions or a thermoset polyester resin formed from an unsaturatedpolyester backbone which is cross linked through the unsaturated linksby a monomer such as styrene, may be employed.

The iron powder and the resinous binder may be blended together at anelevated temperature and then cast in a casting mold in a 4 to 10 tonpress. Likewise, useful shapes of this material may be fabricated byfirst blending together and then extruding through die member. A highproportion of the ferromagnetic iron powder is employed with respect tothe proportion of the binder material. Therewith, the proportion of thematerials is from 1:5 to 1:20 parts by weight of the binder resin to theferromagnetic iron powder. A preferred ferromagnetic material for theconstruction of layer 70 is a wateratomized powdered iron marketed byEaston Company under the trademark SlNTREX-F." This material correspondsin description to the above water-atomized iron powder. A suitableresinous matrix binder is a polyester resin marketed by Cadillac PlasticCompany under trade designation MR37CX.

Another ferromagnetic material which hasbeen employed with considerablesuccess is a mixture of a similar wateratomized iron powder marketedunder designation EZ-46 00" by the Easton Company and having a particlesize range of 7 to 50 microns. The ratio of polyester binder to iron forcasting was 1:10.

The presence of the magnetic material layer in the close proximity tothe converging V-configuration of the edges or edge portions 26 and 28of HO. 1 has been found to greatly increase the efficiency of continuoustube welding by the radiofrequency welding apparatus shown. The use ofthis fluid cooled magnetic material impeder has been particularlyeffective when used in conjunction with aluminum strip material welding.

The presence of the ferromagnetic iron particles at the surface of themagnetic material layer which is contacted by waterflowing in the upperflow channel defined by the magnetic layer and the top semicylindricalpanel 64 does not present an uncontrollable corrosion problem. Theentire surface of the magnetic material layer may be covered over withan exterior coating of a water impermeable material such as I the bindermatrix in order to prevent contact with the water.

.8 Alternatively, precoated iron powders may be employed. Such powdersare coated with a water impermeable polymer and are available in sizesof from 5 to 8 microns. These polymer coated iron particles have an ironcontent of 98 percent, a carbon content of 0.05 percent, an oxygencontent of 0.3 percent and a nitrogen content of 0.5 percent, all byweight. The 8- micron-particle size iron powder is marketed under tradedesignation CO-4" by AntaraChemical Company, while the S-micron sizeparticles are marketed under trade designation GS-6 by the sameorganization.

All of the above particle sizes are small enough so that very limitededdy current flow exists within the individual particles when in theradiofrequency magnetic field. Hence, the radius of such particles issmaller than the skin depth which, if great enough, would providemagnetic shielding Hence, the small diameter of each individual,isolated, particle does not prevent a sufficient thickness to attenuatethe magnetic field by shielding. Yet, due to the high weight proportionof the iron particles, the mass of ferromagnetic material is greatenough to give a high magnetic permeability equivalence to the magneticmaterial layer 70. Due to the surrounding binding matrix, a highresistance to current flow is attained whereby eddy currents are notallowed to flow in a detrimental fashion.

Magnetic field intensity terminating and heat sink block 54 may beconstructed of any common and chemically stable metal which will furnishshielding for radiofrequency magnetic fields. Copper and copper basedalloys are preferred due to their high electrical conductivity and theirability to be bonded to various materials and ability to be machinedinto intricate shapes such as the stepped connection shown in FIG. 4.

By providing for magnetic field intensity termination, the intensitycomponent along the axis of the horn is terminated and the flux linesare deflected away from the surrounding material of horn 20. Themagnetic field intensity component is prevented from penetrating thematerial of horn 20, and, therewith, the undesired heating of the hornis avoided. The use ofa metal of high electrical conductivity for block54 provides electromagnetic shielding due to the generation of eddycurrents by the changing magnetic flux. These eddy currents are of adirection such as to set up induced magnetic fields which compensate oroppose the change in magnetic flux; according to Lenz's law. Due to thelow electrical resistance of such metals, these eddy currents areproduced at or near the surface of block 54, particularly at the highfrequency of the RF coil and, hence, provide practically completeshielding for the material ofthe forming horn 20. The presence of themagnetic field intensity terminating block at the upstream end of themagnetic material layer 70 also prevents local over heating of themagnetic material layer at the upstream end where it would otherwiseabut and contact a substantial mass of the forming horn metal. The goodthermoconductivity of the metals which are also good shielding materialsaids in preventing this local over heating condition.

The material from which the nonmagnetic housing 52 may be constructedcan be any stable thermoplastic or thermosetting resin, such as poly(methylmethacrylate) or castable polyester resins. Poly(methylmethacrylate) under trade designations Lucite and Plexiglas arepreferred. These polymers are nonmagnetic in that they exhibit no grossmagnetism when in a magnetic field. Consequently, they do not alter theimpedance of the current flow paths in the tubular positioned stripmaterial 3 and do not generate heat as do both the magnetic materiallayer 70 and the magnetic field intensity terminating and heat sinkblock 54. These resins or polymers present ease of manufacturing complexshapes by either casting or machining and may also be bonded to othermaterials, such as the magnetic material of layer 70 or the metal block54 with conventional water insoluble resins and glues. The term"nonmagnetic as employed in the present specification and claims isintended to denote an antiferromagnetic material such as the describedmaterials.

Another material from which magnetic material layer 70 and individualelements 74 may be made is a sintered magnetic ferrite material which isavailable in the present market. Such ceramic is manufactured by heatingto a sintering temperature a mixture of ferrous ferrite .or magnetite,Fe 0,, and other metallic oxides in minor proportions which improve themagnetic properties of the magnetite. A general employment is oftransition metal oxides of the general formula MeO. Thin rectangularelements of such material have been illustrated in FIGS. 25 for themagnetic material layer of those FIGS. This material has high volumeresistivity and, hence, is useful as an impeder material. However, itsmachinability is such that it is only difficulty formed into intricateshapes and even in the originally unmachined form, does not havesufficient mechanical strength for many employments.

Referring now to FIG. 6, an impeder device 100 ofthe same generalconfiguration as impeder device 50 of FIG. 1, is shown. Impeder device100 may be substituted in the recess 48 of forming born for impeder 50of FIG. I. This impeder device 100 is a simplified modification ofimpeder device 50, which simplification has been made possible by reasonof the discovery of the novel impeder material of the present invention.

A fluid cooled support member 102 (shown by dotted lines) is providedfor magnetic material layer 104 which is semicylindrical in shape andhas a configured downstream end portion 106. Magnetic material layer 104may be glued or otherwise secured to support member 102. A magneticfield intensity terminating and a heat sink block 108 is attached to theupstream end of support member 102 and has fluid ports 110 and 112extending therethrough for communication with a continuous fluid channelcut in the fluid cooled support member 102.

FIG. 7 shows the fluid entry port 110 and its associated fluid channel114 as well as the return fluid channel 116 and its associated fluidport 112. The undersurface of fluid cooled support member 102 and thehorizontal bottom portions 118 and 120 of magnetic material layer 104are configured for conforming to a recess such as recess 48 of FIG. 1.

FIG. 8 shows the fluid port and fluid channels through which the .fluidcoolant flows for cooling the magnetic material layer 104 and theassociated fluid cooled support member 102. Fluid is forced into fluidport 110 and into a first channel 114 (flow shown by dotted arrow) anddownstream to end wall 122 which has an anvil overhang 124 affixedthereto. The fluid then flows around partition 126 and back along fluidchannel 116 to exit port 112, as shown in FIGS. 6 and 7. Openings 128and 130 are provided at both ends of partition 126, as shown. Theupstream opening 128 does not allow significant fluid passage due to thefact that the lower fluid resistance is through the fluid flow channelsand opening 130 at the downstream end thereof, while the latter opening130 does provide for such fluid flow.

Fluid cooled support member 102 has a magnetic field intensityterminator and'heat sink block 108 affixed to the upstream end thereofand furnishes support for the fluid ports 110 and 112. Block 108 is influidtight engagement with the upstream portions of support member 102.The magnetic material layer 104 is shown in overlying and conformingrelation to support member 102 and may be bonded or secured thereto byglue or mechanical means.

A sealing ring 132 is provided for each of the fluid ports.

FIG. 9 shows magnetic material layer 104 removed from support member 102and block 108. The downstream end of fluid cooled support member 102 hasthe bottom portion 134 tapered inwardly from angular connection 136, aswell as having the horizontal side skirt 138 tapered upwardly fromangular connection 136 to end panel 122. Anvil portion 124 can be seenaffixed to end panel 122.

The downstream end 106 of magnetic material layer 104 is similarlyconfigured in that the undersurface edges 140 on either side thereof aretapered upwardly from angular connection 142 to the main body end 144.An anvil portion 146 is provided for overlying anvil overhang 124 of thesupport member 102. By the configuring of impeder device 100, as

shown in FIGS. 6-9, an impeder device of the same shape as that of FIGS.l-5 is attained.

The greater simplicity of the modified impeder device of FIG. 6 is duein large part to the discovery of the novel magnetic material whichallowed fabrication of magnetic material layer 104. This material is,mentioned above, as being a pressed mixture of iron powder in a resinousbinder which has a high weight proportion of iron therein. The highvolume of the iron present gives a high magnetic permeabilityequivalence to the material and, hence, enables its use in highfrequency alternating magnetic field employments. The iron particles areindividually isolated from one another so that eddy current loss orshielding loss is reduced to a minimum. The material has exceptionalmachinability, a machinability somewhat similar to cast iron, and doesnot present great rust or water corrosion problems. The material isdimensionally stable and, hence, may be employed in much the same manneras cast iron would be employed. In addition to these favorableproperties, the material has a thermal conductivity sufficient tonecessitate cooling only one surface thereof when in the thin crosssection semicylindrical shape of magnetic layer 104, as shown in FIGS.6-9. Hence, a housing device allowing cooling on both sides is notnecessitated by such material as is the ceramic ferrite material whichmay be employed as an alternative to the novel ferromagnetic material inimpeder device 50 of FIGS. 1-5.

In order to manufacture the magnetic material layer 104 of FIGS. 6-9, a4-inch cylinder was cast of a mixture of 600 grams of carbonyl processedpowder (grade No. 2, above) and 72 grams of a thermosetting polyesterbackbone chain resin. The iron powder and the polyester together withthe crosslinking component were stirred at an elevated temperature andthen a catalyst for cross-linking the resin component was added. Thematerial was then placed into a cylindrical mold form and pressed with ahydraulic press at 4-t0ns pressure. After a time sufficient for curing,of several hours, the cylindrical shape was removed. Tests demonstratedthat the 4-inch length had a resistance of about 10,000 ohms and apermeability of 10. The cylindrical shape was then cut into asemicylinder and then a downstream end 106 formed thereon, as shown inFIG. 9. This forming was easily accomplished by machining with ordinarymachining tools.

Another specific example is that of mixing 10 weight parts of a SintrexF iron powder (described above) with a polyester resin (CadillacCompany) in the weight proportions of 10:], respectively. After mixingthe material and adding the catalyst, a press operated from between 4 to10 tons was used to form the cylindrical shape from which the magneticmaterial layer 104 was formed. A somewhat lower equivalent resistancewas obtained from this sample.

A further example is described which is intended to seek an upper rangefor the ferromagnetic material to resinous binder ratio. Accordingly, 20weight parts of Sintrex F iron powder is mixed with the polyester resin(Cadillac Company) in the weight proportions of 20:1, respectively. Thematerial is mixed and the catalyst added. The cylindrical shape isformed by a press operated with a pressure offrom 4 to 10 tons. Asexpected, a somewhat lower equivalent resistance was obtained from thissample.

When uncoated Sintrex iron particles were mixed with a poly(methylmethacrylate) binder at an elevated temperature and cast into acylindrical form, a high conductivity was found. The apparent reason isdue to the lack of encapsulating the individual iron particles with thepoly (methylmethacrylate) resin. To avoid contact of individualparticles so that resistance is high which increases eddy currentlosses, the polymer coated iron particles are preferred.

A preferred modification of the magnetic material layer 104 is to formthe cylindrical in a nonuniform cross section whereby when the magneticmaterial layer 104 is cut therefrom, the topmost portion overlying thesupport member member 102 have a thickness of one-fourth inch. It hasbeen found that the greater amount of impeder material at the topportion where the edges or edge portions of the converging metal areclosest tends to raise the impedance of all paths except those in theimmediate proximity of the edge portions which then has the effect ofchanneling the current flow in the tubular form sheet material to theseedge portions for heating the same to a welding temperature with minimumpower expenditure.

The material of construction for support member 102 and associated block108 may be of copper or a copper alloy. Generally, any common metalwhich serves as a shielding for RF magnetic fields is usable. The copperalloys are particularly advantageous due to their case of machinabilityand the forming of watertight seals therein by the use of low meltingsolders. The high thermal conductivity of copper alloys is extremelyuseful due to the fluid cooled employment of such materials according tothe present invention.

The ferrimagnetic materials such as the sintered ceramic materialemployed for element 74 of FIGS. 2-5 have too low a thermal conductivityfor employment as the magnetic material layer of FIGS. 6-9. It may notbe adequately cooled from a single surface thereof even in thin crosssections. The Curie temperature of such materials is approximately 180C. and would be exceeded in portions of a magnetic material layer of/i-inch thickness overlying a copper support base. This problem ofcooling from a single side only is overcome by employment of the novelferromagnetic material of the iron powder mixed with a low proportion ofa binder resin due to the fact that it may be easily cooled. Thisferromagnetic material has better thermal conductivity and a higherelectrical conductivity than the presently employed ferrimagneticmaterials.

The construction of the magnetic material layer of the finely dividedferromagnetic iron particles together with a resinous binder materialgives a high volume resistivity which effective- 1y limits excessiveeddy currents which would otherwise be induced as in presently employedimpeder materials. If such eddy currents are able to flow within amagnetic material, additional heat results which then increases thecooling problem. The novel material of the present invention has a highmagnetic permeability and, thus, allows a low reluctance path to beestablished for the magnetic flux field generated by induction coil 44.As this magnetic material layer has a Curie temperature above which thematerial becomes paramagnetic, its temperature must be below thiscritical point in order to produce the welding efficiency attainable byuse of the present invention. This magnetic material layer of finelydivided ferromagnetic iron particles together with a resinous binder isnot only characterized by a low electrical conductivity, but alsopossesses low thermal conductivity which then effectively limits thesize and thickness of the material which may be used as an impeder. 1fthe thickness of the impeder is not restricted, a heat buildup in thecenter of the impeder may result which may take the material in thatregion above the Curie temperature. However, such ferromagneticmaterials exhibit a saturation flux density and, thus, a sufficientthickness must be employed to prevent saturation in the radiofrequencymagnetic field.

In practice, forming horn 20 may be constructed of stainless steel,copper, aluminum or a resin material such as fiberglasresin composites.The metallic materials tend to rise in temperature during welding to anequilibrium level and the heat generated thereby may adversely affectthe permeability of any magnetic material associated therewith, byraising the same above its Curie point. The impeder device 50 or impederdevice effectively eliminates this problem by placing the magnetic fieldintensity terminating and heat sink blocks 54 and 108, respectively,between the magnetic material layers and .the material of horn 20. Thecoolant fluid for cooling the impeder device may be either water, oil orother conventional medium.

lmpeder devices of the above type have been tested and found to increasethe welding efficiency of welding lines without impeders several fold.Welding speeds of 400 feet per minute have been attained. For themanufacture of cylindrical food container bodies of 5 inches length,this welding speed amounts to 1,000 cans per minute which is abovecommercial rates of production in present technology. By increasing thefluid coolant flow rate and by increasing the cross-sectional area ofthe magnetic material layers of impeder devices 50 and 100, weldingspeeds between 400 to 2,000 feet per minute are expected.

As the welding speed as above set out may be increased by enlarging thecross-sectional area of the magnetic material layer, the above weldingspeeds which are attainable with the proportions of cross-sectional areato length demonstrated by the drawings is not to be taken as alimitation of the present invention.

It is obvious that the illustrative practices are not restrictive; andthat the invention may be practiced in many ways within the scope oftheappended claimed subject matter. In particular, at low power levelswherein low voltage and current are supplied to the RF induction coiland at low welding speeds, no particular cooling means other thanconduction cooling by the air moving along the tubular formed stripmaterial and by conduction through the associated parts of the impederdevice and forming horn need be provided.

What we claim is:

1. In a radiofrequency welding apparatus having a radiofrequency heatingmeans and a horn for positioning opposite edge portions of stripmaterial for welding, the improvement of an impeder member constructedof a composition of matter having a high magnetic permeabilitycomprising a uniform mixture of a particulated ferromagnetic materialand a resinous binder in the weight ratio range of from about 5:1 to

about 20:1, respectively.

2. The impeder according to claim 1 in which said particulatedferromagnetic material is powdered water-atomized iron.

3. The impeder according to claim 1 in which said particulatedferromagnetic material is carbonyl processed iron.

4. The impeder according to claim lin which said resinous binder is across-linked polyester backbone polymer.

5.,The impeder according to claim 2 in which said resinous binder is across-linked polyester backbone polymer.

6. The impeder according to claim 7, wherein said impeder membercomprises a magnetic material layer supportively positioned near aportion of the apparatus where said opposite edge portions of said stripmaterial may be positioned by said horn.

7. The impeder member according to claim 13 wherein said layer isconstructed of a powered alpha-iron and a polyester resin binder.

1. In a radiofrequency welding apparatus having a radiofrequency heatingmeans and a horn for positioning opposite edge portions of stripmaterial for welding, the improvement of an impeder member constructedof a composition of matter having a high magnetic permeabilitycomprising a uniform mixture of a particulated ferromagnetic materialand a resinous binder in the weight ratio range of from about 5:1 toabout 20:1, respectively.
 2. The impeder according to claim 1 in whichsaid particulated ferromagnetic material is powdered water-atomizediron.
 3. The impeder according to claim 1 in which said particulatedferromagnetic material is carbonyl processed iron.
 4. The impederaccording to claim 1 in which said resinous binder is a cross-linkedpolyester backbone polymer.
 5. The impeder according to claim 2 in whichsaid resinous binder is a cross-linked polyester backbone polymer. 6.The impeder according to claim 7, wherein said impeder member comprisesa magnetic material layer supportively positioned near a portion of theapparatus where said opposite edge portions of said strip material maybe positioned by said horn.
 7. The impeder member according to claim 13wherein said layer is constructed of a powered alpha-iron and apolyester resin binder.